1. Field of the Invention
This invention relates to the making of a wide variety of metal products from molten metal using such processes as extraction of the metal from ore, purification processes, and mechanical working processes such as continuous casting and, more particularly, to improving the manufacturing method and the quality of the metal product, and in particular copper, by using an improved probe body in a gas measurement system used to measure the gas content of the molten metal during metal processing steps. The measurement system comprises an analyzer instrument and an improved long lasting probe body wherein the probe body is inserted into the molten metal at any of a number of process steps in the metal product making process and a carrier gas is cycled in a circuit between the analyzer instrument and the probe body with the analyzer electronically comparing a reference value with the value obtained by a mixture of the carrier gas and gases from the molten metal entrapped or formed in the probe body to provide a gas measurement content reading for the molten metal.
2. Description of Related Art
The production of metals such as steel involves a number of processing steps from extraction of iron from iron ore to the actual steel making step wherein molten iron is treated with oxygen and carbon to form the steel. In the steel making process and likewise in the copper making or other metal making processes, molten metals are processed and formed into a solid product. The manufacture of copper products by continuous casting is well-known in the art and the manufacturing process is described in the "Extractive Metallurgy of Coppers" by A. K. Biswas and W. G. Davenport, First edition, Chapter 17, pages 336-368, the disclosure of which is hereby incorporated by reference. The following description for convenience will be directed to the making of copper products although it will be appreciated by those skilled in the art that the method and apparatus of the invention may be used for other metal making processes where it is important to measure the gas content of the molten metal.
As described in Phillips et al., U.S. Pat. No. 3,199,977, which patent is hereby incorporated by reference, cathodes or other forms of pure copper are melted in a furnace and the molten copper fed to a holding furnace for casting. The Asarco shaft furnace is predominately employed and the copper is placed in the furnace at the top and is heated and melted as it descends down the shaft. The heat is provided by impinging and ascending combustion gases produced in burners near the bottom of the furnace.
The furnace is primarily a melting unit and the burners and combustion gases are such that the copper is generally not oxidized during melting. This is achieved by using specially designed burners which insure that unconsumed oxygen in the burner does not enter the furnace shaft and by controlling the fuel/air ratio of the burners to provide a slightly reducing atmosphere in the furnace. In general, the fuel/air ratio is controlled to provide a reducing flame having a hydrogen content of the combusted fuel of up to about 3% by volume, usually 1%-3%.
There is generally no holding capacity in the furnace bottom and the molten copper flows immediately into a separate burner fired holding furnace. In many installations, the launder connecting the shaft furnace and the holding furnace is also burner fired to likewise maintain the temperature of the copper and to minimize unwanted oxidation of the copper.
The molten copper in the holding furnace is then fed to a continuous caster, such as a Properzi or Southwire wheel caster or a Hazelett twin belt caster. In the Hazelett caster, molten copper is cast between two coincidentally moving steel belts and the casting, usually a bar shape, is fed directly into a rod-rolling mill. The rod is normally discharged into a pickling unit, coiled, and stored.
U.S. Pat. No. 4,290,823 granted to J. Dompas shows the basic continuous casting process for manufacturing copper and this patent is hereby incorporated by reference. The Dompas process produces an oxygen containing rod product which purportedly has the advantages of oxygen free copper (ductility) and the annealing capacity of tough pitch copper. The process uses a solid electrolyte containing an electrochemical cell to analyze the oxygen content of the molten copper in the holding furnace and adjusts the fuel/air ratio of the holding zone burners to maintain the desired oxygen level.
An article entitled Continuous Casting and Rolling of Copper Rod at the M. H. Olen Copper Refiner Uses No Wheel", by J. M. A. Dompas, J. G. Smets and J. R. Schoofs (Wire Journal, September 1974, pages 118-132) also shows a typical rod making process.
Regardless of the particular processes and controls used, the main concern is to enhance the quality of the final copper product and meet standards relating to appearance (surface quality), electrical conductivity, and physical behavior during fabrication and use. While various automatic mechanical type control techniques such as a surface quality detector are used in continuous casting systems, these techniques provide a relatively simple system for monitoring surface quality and do not control the more significant variables within the process directly or indirectly.
The same problems are encountered in making a wide variety of metals including steel and it is important to control operating parameters to provide a quality metal product. For example, hydrogen enbrittlement is a serious concern in steel manufacture and hydrogen control is very important in the steel making process. Degassing operations are an important process step in steel making and a reliable and efficient gas analyzer is essential for this purpose. Degassing may be performed using a wide variety of processes such as vacuum degassing, sparging the molten metal with an inert gas, such as nitrogen, or reacting the molten metal with a material that removes the unwanted gas, such as H.sub.2. Regardless of the process used or parameters to be controlled, accurate gas measurement of the molten metal is essential for the process.
A number of gas measurement systems have been developed over the years. One gas measuring system which is particularly desirable uses a probe body immersed in molten metal to determine the concentration of the gas present in the metal as described in U.S. Pat. No. 4,907,440 to Martin et al., the disclosure of which is incorporated herein by reference. This gas measuring system comprises a combination of an immersion probe which consists of a gas-permeable, liquid-metal-impervious material of sufficient heat resistance to withstand immersion in the molten metal and an analyzer instrument. The probe body has a gas inlet to its interior and a gas outlet with the gas inlet and gas outlet being spaced from one another so that gas passing from the inlet to the outlet traverses a substantial portion of the probe body interior for entrainment of gas diffusing to the interior of the body from the molten metal. The probe body is immersed in the molten metal and a carrier gas circulated into the probe body to entrain gas that has diffused into the probe body from the molten metal. The carrier gas-entrained mixture is then passed through the outlet to an analyzer which measures the concentration of the entrained gas by electronic means. The gas measuring system is very effective for measuring the gas content of molten metal and a number of improvements have been made to the time to equilibrium and accuracy of the system particularly in the type carrier gas that is used to entrain the gas diffusing into the probe body from the molten metal.
A serious deficiency of the gas measuring system of Martin et al. however, is that the probe body is not very resistant to the deleterious effects of the molten metal. The probe body is damaged by the molten metal (e.g., disintegrates) and lasts for only a short time such as less than eight hours and often less than one hour when immersed in molten copper. The probe body must therefore be replaced frequently which is expensive and time consuming and which decreases the overall efficiency of the metal making process.
Bearing in mind the problems and deficiencies of the prior art, it is an object of the present invention to provide an improved method and gas analyzer system for measuring the gas content of molten metals, particularly hydrogen in molten copper and steel, which gas measurements may be used to control or monitor the various steps of a metal making process to control the gas of the molten metal.
It is a further object of the present invention to provide a long lasting probe body for use with a molten metal gas measurement system.
Another object of the invention is to provide an improved method for the making of long operating life probe bodies for use in molten metal gas measurement systems.
A further object of the invention is to the use of a gas analyzer system in molten metal operations including degassing operations to measure the gas content of the molten metal.
Another object of the invention is to make metals using the method and gas measurement system of the invention.
An additional object of the invention is to provide a gas analyzer system for measuring the gas content of molten metals.
Other objects and advantages of the present invention will become apparent from the following detailed description.